RBD Basics

RAM Commander displays each RBD in a separate window.

RBDs are graphically composed of the following elements:

Parallel section	A redundancy section containing n items. Parallel sections fail when all its items fail at the same time.
Parallel branch	A series of elements in parallel with other elements or a group of elements
SubRBD	A collapsed representation of an RBD.
Regular item	Any item with reliability data.
k-out-of-n section	A parallel section with n items. A k-out-of-n section is functional when k or more of the n elements are operational. The section fails when n ? k + 1 items fail at the same time.
Insertion node	A place to insert new RBD elements

rbd_diagram_with tags

You add elements to the RBD diagram in a manner such that each element represents a reliability stage in the entire system.The overall system fails when there is no path from the input node to the output node with all its elements operational.

As you build the RBD, you must consider how true it is to the real system. For instance, an automobile stops functioning when one of its tires fails. The appropriate RBD for this situation is placing a k-out-of-n element, where k=4 and n=4. Using four parallel branches, one for each tire, is inappropriate, since the RBD would still be functional when one of the tires fails.

Each RBD element/block has time to failure parameters (for example MTBF) and may have time to repair parameters (for example Mct).

The same block ("identical" block with the same Ref.Des. value) may be repeated multiple times in the diagram. If "Identical" calculation or simulation is specified, algorithm assumes that identical blocks represent the same physical system block and it is taken into account by calculation.

RBD diagram may contain another nested RBD diagrams (Sub-RBDs).

When RBD is built and time to failure/repair parameters for all elements are specified, RBD calculation may be performed to calculate Reliability, Availability and MTBCF.